Carrier wave receiver



May 23, 1933.

P. O. FARNHAM CARRIER WAVE RECEIVER Filed Dec. 21, 1951 Patented May 23, 1933 emme PAUL o. remnant, or noomonnnw :mnsn nssrenon rename moomrcr LABORATORIES, JENGOREOBATED, 0F BOONTON, NEW JERSEY, A CORPORATION 0! NEW, JERSEY 0 wave anonrvnn Application filed December 21, 1931. Serial No. 582,407.

This invention relates to carrier Wave receivers and more particularly to receiver's including a simple, eiiicient and inexpensive automatic volume control for rendering the rectified output substantially independent of the strength of the received slgnals.

An object of the invention is to provide an improved carrier Wave receiver in whlch a single tube performs the function of a demodulator, a rectifier for supplying an automatic volue control voltage and an audio frequency amplifier. A further object 1s to provide a carrier wave recelver m. which a multiple element tube. constitutes a (llode rectifier which delivers an audio frequency output to a local. circuit and a rectified carrier voltage to a gain control circuit, and

an audio frequency amplifier.

These and other ob'ects of the invention will be apparent from the followmg specification when: taken with the accompanying drawing in which the single view is a fragmentary ircuit diagram of a 'ece1ver embodying t e invention.

In the drawing, the reference numeral 1 identifies a carrier wave amplifier which includes one or more tubes 2 which have input circuits including inductances 3 tuned by condensers 4 which may be, and preferably are, similar sections of a gang condenser. The low potential terminals of the inductances 3 are grounded on their respective cathodes for carrier. frequencies by condensers 5 and are connected to each other and to an automatic gain -control voltage line 6 that leads to the novel detector stage that embodies the present invention.

The particular electrical design and the mechanical construction of the carrier wave amplifier do not form a part of the invention. The amplified signal voltage develas illustrated, a conventional screen grid tube having a cathode K, a control grid G screen grid Gr and a plate P, or it ma include additional grid elements in accor ance with known tube practice. As will be appar-- ent from the following description, the tube does not function as a conventional screen grid tube but as a tube having a cathode, a

control grid and two anodes.

The input circuit 8, 9 is not, however,

connected between the cathode K and 0011- trol grid G but the high potential terminal of the input circuit is connected to the plate P and the lower potential terminal is connected to cathode K through the resistor 11 that is by-passed, for carrier frequencies, by a condenser 12. With this circuit arran ement, rectification of amodulated carrier frequency voltage impressed on the tube from the tuned input circuit 8, 9 takes place by the diode action between anode l? and cathode K. The modulation com onent of the carrier voltage develops there y an aud1o frequency component which is im ressed on the control grid G for ampli cation.

The average carrier level develops a direct current component of voltage across resistor 11 which is fed back to furnish automatic grid bias for the preceding amplifier stages.

The audio frequency voltage developed across the resistance 11 is impressed upon the control grid G by connecting the grid G to. the point 13, i. e, the junction of inductance 8 and resistance 11. This connection includes a condenser 14 to isolate the grid from the direct current component of the rectified carrier voltage, and a filter comprising a resistance 15 shunted to ground by condenser 16, which filter prevents any appreciable carrier frequency voltage from reaching the control grid G A grid bias appropriate for audio frequency amplification is impressed on grid G, from a source, indicated as -C, through the bias resistor 17. The primary winding of an audio frequency transformer T is connected between the screen grid G and a source of positive potential +B, and the element G therefore acts as the anode of a triode amplifier having a cathode 'K and control grid G -The direct current component of the rectified carrier voltage developed across resistor 11 by the diode action of plate P and cathode K is impressed upon the automat1c gain control lead 6 by a connection 18 extending from point 13 to lead 6 through the alternating current filter network 19.

The following values are given as indicative of a design suitable for use in the reception of carrier wave signals in the frequency band of from 500 to 1500 kilocycles;

Resistance 11=200,000 ohms Resistance 15=100,000 ohms Capacity 12=500 micromicrofarads Capacity 14=5,000 micromicrofarads Capacity 16=l00 micromicrofarads Screen grid voltage, +B,=10O volts Control grid bias, C,= 5 volts Inductance 8 and tuning condenser 9 were substantially identical with the corresponding tuning elements 3, 4, respectively, of the carrier'wave amplifier stages, and the transformer T was designed to give satisfactory audio fidelity characteristics.

As compared with the conventional use of a diode rectifier as a demodulator and a source of gain control voltage, the novel arrangement retains the advantage of the linear characteristics of the diode detector and possesses the further advantage that the rectifier signal is amplified at audio frequency, thus increasin the sensitivity of the receiver. Further a vantages arise from the fact that the characteristics of the audio amplifier are not affected by value of the carrier input since the rectified carrier voltage is by-passed from control grid G by the condenser 12. As the primary of the audio transformer T is in the output circuit of an amplifier, and not a detector, the transformer may Le of comparatively inexpensive costruction as it is not necessary to employ a high impedance primary.

In the usual plate circuit rectifying detectors, the tube impedance across which which the audio load is connected is relatively low since the direct current poten tials on the control grid and screen grid circuits are appropriate for amplification, not detection. Good fidelity is therefore obtained when the audio frequency transformer has an' impedance substantially lower than that of the transformers which, when located in a detector output circuit, would give equally good results.

I claim: a

1. The combination with a carrier wave amplifier and a tube having cathode, control grid, screen rid and plate elements, of circuit connect1ons for impressing between the cathode and plate elements the amplified carrier wave voltage developed by said amplifier, said circuit connections including a resistor across which rectified direct current and alternating current voltages are developed by the diode rectifier action of said cathode and plate elements,

means for impressing the said alternatin current voltage between the control grid and cathode elements, and means for return ing to said amplifier a gain control voltage derivedfrom andpro ortional to the rectified carrier voltage eveloped across said resistor.

2. The combination with a carrier wave amplifier and a tube having a cathode, first anode, control grid, and second anode; of circuit connections for impressing between the cathode and first anode elements the amplified carrier wave voltage developed by said amplifier, said circuit connections including a resistor across which rectified direct current and alternating current voltages are developed by the diode rectifier action of said cathode and first anode elements, means for impressing the said alternatin current voltage between the control gri and cathode elements, and means for returning to said amplifier a gain control voltage derived from and proportional to the rectified carrier voltage developed across said resistor,

3. In a radio receiver, the combination with a carrier wave amplifier; of a tube having a cathode, a rectifier anode, a control grid, and a positivel polarized output anode; an input circuit or said tube upon which the carrier wave output of said amlifier is impressed; said input circuit being connected between the cathode and the rectifier anode and including, in series, .a carrier-wave coupling circuit, and a resistor shunted by a carrier-wave b pass condenser; means groundin the tu e cathode for audio and carrier requencies, a coupling capacity between control grid and the unction of said resistor and carrier-wave coupling circuit; an audio frequency output circuit connected between the cathode and the ositively polarized output electrode; and means, im ressing between said control grid and cat ode a direct current bias potential effective to secure amplification in the audio frequency output circuit of audio frequency variations impressed upon said control grid.

4. In a carrier wave receiver, the combination with a carrier wave amplifier, of a tube having a cathode, control grid, screen grid and plate elements; an input circuit emme tor said tube and upon which the amplified carrier wave output of said amplifier is imressed,'said input circuit being connected tween the late and cathode elements of said tube an includin in series, a tuned circuit and a resistor s unted by a carrier wave by-pass condenser, means grounding the tube cathode for audio and carrier frequencies, a capacity between control grid and the junction of said resistor and tuned circuit, an audio fre uency output circuit connected between e screen grid and cathode, and means impressing between said control grid and cathode a direct current M bias potential eflective to secure am lification in the screen grid circuit of an o frequelcy variations impressed on said control gri 5. The invention as set forth in claim 4,

wherein said audio frequency output circuit.

comprises an inductance and a source of direct current potential, said inductance having an impedance not less than and of the order of the internal tube impedance between screen grid and cathode over the useful audio frequency range, and said direct current potential being efiective to secure amplificae tion of the audid fre uenc variations impressed on said cdntro l gri 1 o 6. The invention as set forth in claim 4,

in combination with means' includinga direct current circuit connected across said resistor for automatically varyin the gain of said amplifier as a function 0 the recti' 5 fied carrier voltage'developed across said ir i "h rim" testimonyw ereo a xm si ature. I 2 7 PAUL O. 

